output/Bigram.java
package input ;
import java . util . * ;
// Can you spot the bug? (Page 188)
public class Bigram {
private final char first ;
private final char second ;
public Bigram ( char first , char second ) {
this . first = first ;
this . second = second ;
}
public boolean equals ( Bigram b )  {
return b . first == first && b . second == second ;
}
public int hashCode ( ) {
return 31 * first + second ;
}
public static void main ( String [ ] args )  {
Set < Bigram > s = new HashSet < > ( ) ;
for ( int i = 0 ; i < 10 ; i ++ )
for ( char ch = 'a' ; ch <= 'z' ; ch ++ )
s . add ( new Bigram ( ch , ch ) ) ;
System . out . println ( s . size ( ) ) ;
}}

